Hot-fill bottles and other such containers are used to package liquids which must be stored and sealed in the container while hot to provide adequate sterilization. For example, containers of plastic are filled with liquid products under slight positive pressure and at temperatures approaching the boiling point of water. The bottles are immediately capped to ensure sterilization.
In the case of filling glass bottles in a like manner, the cooling of the liquid product usually creates a vacuum which collapses a flexible metal cap. However, due to the rigidity of the glass bottle, shrinkage of the product as it cools and creation of negative internal pressure does not significantly affect such rigid containers.
In the case of flexible plastic hot-fill containers, however, even slight negative internal pressure caused by cooling and gas volume reduction above the liquid product is a serious problem. Plastic bottles which are not adequately reinforced with structural enhancements are often unsuitable for hot-fill products since they collapse and create creases and ridges in the body of the flexible plastic bottles. Labels do not adhere and customers are hesitant to purchase products which appear as if they have been damaged.
Accordingly, the prior art includes several plastic bottles for hot-fill use which provide collapsible vacuum panels to accommodate the volume reduction on shrinkage of the hot-fill product.
U.S. Pat. No. 5,704,503 to Krishnakumar et al. issued Jan. 6, 1998 describes one such hot-fillable plastic container with collapsible panels under the label area. It has been found in the prior art that the provision of collapsible panels alone is generally insufficient to ensure shape integrity, adequate labeling and maintenance of the cylindrical label area. In U.S. Pat. No. 5,704,503, vertical reinforcing ridges and horizontal reinforcing bands are provided to enhance the structural rigidity of areas immediately adjacent to the collapsible panels.
Another example of collapsible panels is shown in U.S. Pat. No. 5,054,623 to Alberghini et al. In Alberghini, the inventor provides two rows of similar collapsible panels and a single triangular reinforcing ridge between the circumferential array of panels. Other examples are shown in U.S. Design Pat. No. 321,830 to York et al. and U.S. Design Pat. No. 366,417 to Semersky. Various designs have also been developed in the prior art including hoop reinforcing circumferential ridges for flexible plastic bottles. Examples are shown in U.S. Design Pat. No. 347,391 to Guertin and U.S. Design Pat. No. 322,562 to Narsutis.
It can be seen from the wide assortment of hot-fill bottle designs in the prior art that numerous combinations of: collapsible panels; reinforcing circumferential ridges; and axially extending posts, are used to to accommodate the vacuum of the cooled state and to maintain the substantially cylindrical shape of label areas of the bottle body.
Despite the complex designs proposed in the prior art, the inventors have found that collapse under vacuum still occurs in localized areas. Mold making costs rise dramatically when numerous ridges and complex shapes are machined in the mold surfaces. Structural viability of such shape complexities is often not based on clear scientific principles, but on trial and error. Not only must complex shapes in the plastic molds be produced at relatively high cost by skilled workers, but these shapes must be polished to produce a clear product with the desired surface finish and must be maintained in extremely good condition to ensure product quality. Design complexity also effects the flow of hot plastic during blow molding. In general, a simple bottle design, that accomplishes the purpose of allowing vacuum collapse in a controlled manner, is desirable in order to reduce manufacturing and maintenance costs.
An object of this invention is to rationalize the many complex designs of the prior art into a simple practical workable design. In this manner costs involved in producing molds and maintaining the quality of the resulting bottle are reduced.
It is a further purpose of the invention to provide a hot-fill bottle with capacity to reduce volume while retaining structural rigidity in a simple design which can be adapted to various shapes of hot-fill bottles.